Differences in the time-course of postnatal development of the peripheral neural vasoconstrictor and local vasodilator systems in the regulation of blood flow will be investigated in piglets of various ages under anesthesia. The pressure-flow relationship in the in situ perfused organ will be determined before and during or after specific experimental interventions designed to elicit changes in neural or autoregulatory control. Arterial pressure will be registered by strain-gauge transducer, and flow by non-cannulating electromagnetic transducer. The role of neural activity will be assessed in experiments involving denervation and stimulation of sympathetic efferent fibers. The role of local vasodilator mechanisms will be assessed in experiments utilizing infusion of physiological vasoactive compounds into the artery supplying an organ. Differences between neurally and locally mediated responses at each age will be established by statistical analysis of a population of piglets in several age groups compared with a group of adult swine. This broad program will be initiated with a study of the renal circulation.